Vibration type angular velocity sensors are used to detect rotation, sidewise slipping, etc. of vehicles. For example, according to a vehicle stabilization control system or a four-wheel steering angle control system, sidewise slipping of a vehicle is detected on the basis of an angular velocity or the like detected by a vibration type angular velocity sensor to detect an abnormality state of the vehicle, and a brake is controlled on the basis of the detection result, so that the vehicle can travel safely.
According to vibration type angular velocity sensors, an AC voltage is applied from a driving circuit to a vibrator to drive the vibrator in a driving axis direction, the signal corresponding to a displacement of the vibrator occurring in a detection axis direction perpendicular to the driving axis direction is detected, and an angular velocity signal is produced on the basis of the signal corresponding to the detected displacement.
The velocity of an object having a mass M in the X-axis direction is represented by v-vector, the direction perpendicular to the v-direction is set as the Y-axis direction and the direction perpendicular to both the X-axis and the Y-axis is set as the Z-axis. When an angular velocity Ω is generated around the Z-axis, Coriolis force 2·M·(Ω×v) acts on the object in the Y-axis direction. Here, Ω represents the vector in the Z axis direction and “×” represents outer product. Therefore, a displacement occurs in the detection axis (Y-axis) because the vibrator is vibrated in the driving axis (X-axis) direction, the signal corresponding to the displacement occurring in the vibrator in the detection axis (Y-axis) direction is produced, and finally an angular velocity signal is produced on the basis of the signal corresponding to the displacement of the vibrator.
The signal component of Coriolis force is proportional to the velocity v of the object. Therefore, when the vibrator is vibrated at a predetermined frequency, the signal component appears as a component whose phase is shifted from the displacement in the driving axis direction of the vibrator by 90 degrees like it vibrates in the detection axis direction.
It has been found in this kind of vibration type angular velocity sensor that even when no angular velocity Ω is applied around the Z-axis, an extraneous or unnecessary vibration component appears in the detection axis direction due to an effect such as a mechanical dimensional error or the like of the vibrator. This extraneous vibration component is varied by external disturbance such as temperature or the like, and thus the vibrator is generally adjusted so as to reduce the extraneous vibration. If no adjustment is made, the travel characteristic of the vehicle in the above system is controlled remarkably unstably, and this is not desirable.
Therefore, U.S. Pat. No. 5,987,987 No. (JP-A-11-351874) discloses a method of adjusting extraneous vibration of the vibrator of a vibration type angular velocity sensor. According to this adjustment method, extraneous vibration occurring in the detection axis direction of the vibrator can be reduced by mechanically trimming the ridge line of the base portion of the vibrator as shown in FIG. 5.
However, the method of mechanically trimming the ridge line of the base portion of the vibrator needs a trimmer for trimming the vibrator and a suction device for sucking trimmed-out dust absorbed in the sensor main body on the vibrator in the adjustment work. Furthermore, if an adjustment error occurs due to excessive trimming of the vibrator, it is difficult to re-adjust the extraneous vibration. In addition, trimming of the vibrator may apply a mechanical damage to the vibrator.